Chemistry Lect 6

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Author:
laskiru
ID:
59048
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Chemistry Lect 6
Updated:
2011-01-11 15:03:57
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Acid Base Chemistry
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Acid Base Chemistry
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  1. Indicators usually change color...
    within +/- 1 pH point of their pKa
  2. Bronstead Lowry Acid and Base
    • Acid: donates a proton
    • Base: accepts a proton
  3. Lewis Acid and Base
    • Acid: accepts a pair of electrons
    • Base: donates a pair of electrons
  4. Arrhenius Acid and Base
    • Acid: produces a hydrogen ion (H+) in aqueous solu'n
    • Base: produces a hydroxide ion (OH-) in aqueous solu'n
  5. pH
    • pH = -log [ H+]
    • i.e. 4*10-3 --> pH is lower than 3 but higher than 2
    • pH = -log (4*10-3) = 2.4
  6. Acid Strength Related to Conj. Base
    • The stronger the acid, the weaker the conj. base
    • ** a weak acid however may have a weak or strong conj. base **
  7. Strong Acids
    • Hydroiodic - HI
    • Hydrobromic - HBr
    • Hydrochloric - HCl
    • Nitric - HNO3
    • Perchloric - HClO4
    • Chloric - HClO3
    • Sulfuric - H2SO4
  8. Strong Bases
    • Sodium Hydroxide - NaOH
    • Potassium Hydroxide - KOH
    • Amide Ion - NH2-
    • Hydride Ion - H-
    • Calcium Hydroxide - Ca(OH)2
    • Sodium Oxide - Na2O
    • Calcium Oxide - CaO
  9. Acids dissociate ___ in higher concentrated solution.
    Less
  10. Acid Strength is Dependent On:
    • Bond Strength: the higher the bond strength, the harder it is to remove the proton and the weaker the acid is
    • Bond Polarity: the more polar, the easier it is to remove the proton, the more acidic the acid is
    • Stability of Conj. Base: the more stable the more acidic
  11. Common Acids Compare Strength
    • HF < HCl < HBr < HI
    • least --------------> most
  12. Hydrides
    • Metal Hydrides = basic or neutral
    • Non-Metal Hydrides = acidic or neutral
    • acidity tends to increase as we move down the periodic table
  13. Equilibrium Constants For Acid-Base Rxns
    • Kw = [H+][OH-] = 10-14
    • pH + pOH = pKw = 14
    • Ka = [H+][A-] / [HA]
    • Kb = [OH-][HA] / [A-]
    • Kb * Ka = Kw
  14. Equivalence Pt
    • equal equivalents of acid/base and its conjugate
    • 100% A- (conj)
  15. Half Equivalence Point
    • exactly half of the acid/base has been neutralized
    • solu'n is considered buffered
    • pH = pKa
    • 50% HA and 50% A-
  16. Henderson Hasselbalch
    • pH = pKa + log [A-]/[HA]
    • remember log (1) = 0 --> this is why the 1/2 equiv. pt is pH = pKa
  17. Indicators
    • The range of the indicator is pH = pKa +/- 1
    • endpoint - when the indicator changes color
    • usually you choose and indicator whose range will cover the equivalence point
  18. Polyprotic Titrations
    Assume the first proton completely dissociates before the second starts
  19. To make a buffered solution we:
    • start with an acid whose pKa is closes to the pH at which we want the buffer to be
    • mix equal amounts of the acid and its conjugate base

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